1. Field of the Invention.
The present invention relates to disk drives; more particularly, to hard (or fixed) disk drives.
2. Description of the Related Art.
Developments in personal computers, portable computers and lap top computers have prompted reductions in the size and increases in memory capacity of disk drives. Attempts to provide further reductions in the size and weight, and increases in durability and memory capacity of existing disk drives have been met with limited success. The size (particularly the height) and weight of fixed or hard disk drives and the inability of existing hard disk drives to withstand physical shocks and/or vibrations have been factors which have prevented the incorporation of fixed disks in lap-top and in some cases even larger portable computers.
Existing disk drives incorporate a large number of mechanical parts. Each part in a disk drive also represents an increase in the weight of the drive and the space occupied by the drive. A large number of mechanical components makes manufacturing difficult and expensive and increases the possibility and probability of the mechanical failure of the drive. Importantly, the number of mechanical components is related to the ability of the drive to survive physical shocks and vibrations.
Resistance to physical shocks and vibrations is critical to protecting the disk or disks, the head or heads, and the various bearings in a disk drive from damage; in particular, it is necessary to prevent damage to the disks which can cause a loss of data, and damage to the heads or the bearings which can end the life of a drive, resulting in a total loss of data. Prior disk drives, however, have limited resistance to physical shocks. Resistance to physical shocks is of paramount importance in portable computers.
In conventional drives mechanical distortion or flexing of the mechanical components of a disk drive which support the heads and disks causes tracking problems by moving the heads, which are mounted at one point on the supporting components, relative to the disk, which is mounted at another point on the supporting components. The heads associated with the top and bottom surfaces of a disk can move relative to the disk to the point where the different heads are in different cylinders--a cylinder being defined as a vertical segment representing the same track on the top and bottom surfaces of a disk. This problem is known as mechanical off-track. This problem is compounded by increased track densities.
Another problem with prior disk drives is the difficulty in sealing the drive to protect the disks from contaminants. This difficulty arises in part, from the large number of points at which access is provided to the environment in which the disk resides. These access points are utilized to bring to the interior of the disk drive electrical circuits which provide current to the motor which rotates the disk, transmit data signals to and from heads which read and record information on the disks, and in some instances, provide current to a voice coil for positioning the head (or heads) with respect to the disk or disks.
Many of these disadvantages of prior disk drives are attributable to the casing--a three-dimensional casting or so-called "toilet bowl"--in which the disks reside. Such a casing is a large, three dimensional piece of cast metal, usually aluminum, having a round portion where the disks reside--hence the name "toilet bowl." A top plate covers the entire open top of the casing, forming a seal therewith. The spindle on which the disks rotate is supported by and extends through both the casing and the cover.
The protrusion of the spindle through the casing and the cover provides possible points of entry for contaminants. Further, in disk drives using stepper motors to position the heads with respect to the disk, the stepper motor is located outside of the casing, requiring a seal between the stepper motor and the casing. Acknowledging the existence of points where contaminants can enter the disk drive, manufacturers of conventional disk drives provide a breather filter and design the disk drives so that the rotation of the disks causes the disk drives to exhaust air through leaks in the seals and to intake air only through the breather filter. However, a fairly course filter must be provided in the breather filter for a flow of air to exist, and thus contaminants enter the disk drive through the filter paper.
A cast casing is difficult to manufacture with precision, particularly the location of mounting points for elements of the drive supported by the casing. Mounting holes must be drilled after the casing is cast, and the mounting holes must be aligned with the casing and with each other. More importantly, however, a three-dimensional, cast casing flexes due to thermal stresses causing the above-mentioned mechanical off-track problems.
In conventional disk drives which use a voice coil to pivot an actuator arm in order to position the heads with respect to the disk, a flex circuit, having one end attached to the actuator arm and the other end attached to a fixed point in the disk drive, transfers the information signals to and from the heads. The standard orientation of such a flex circuit is a loop extending away from the disk. The distance between the point at which the flex circuit is attached to the actuator and the end of the disk drive is limited, and thus the radius of the arc or curve of the flex circuit is small and the length of the flex circuit itself is limited. Therefore, the entire flex circuit moves when the actuator arm is pivoted and a torque is exerted on the actuator arm by the flex circuit. The torque exerted on the actuator arm must be compensated for, either added to or subtracted from the torque created by the voice coil, when performing a seek operation. This compensation is complicated by the fact that the torque exerted on the actuator by the flex circuit varies with the position of the actuator.
Various types of locking (or latch) devices have been used to lock the arm of a voice coil in a particular position when the disk drive is not operating. The trend in latch devices is to utilize a high power unit which is separately assembled to provide reliability. However, high power latch devices generate a large amount of heat which is not desirable in a disk drive or any other area in a computer. Further, the operation of conventional latch devices can be position dependent. Thus, the orientation of the disk drive and the computer in which the disk drive is installed could effect the reliability of the latch device. Such a positional dependence of reliability is not satisfactory for portable computers.